Method for fighting dust and noxious gases after blasts in mines

ABSTRACT

Finely-divided calcium chloride and/or magnesium chloride are employed to suppress and remove dust and noxious gases generated during blasting by sealing the blast-holes with these salts.

United States Patent 1 Lewer METHOD FOR FIGHTING DUST AND NOXIOUS GASES AFTER BLASTS IN MINES [75 Inventor: Hans Lewer, WitteY1-Arinen Germany [73] Assignee; Chemische Fabrik Kalk GmbH 22 Filed: July 1, 1970 [21] Appl. No.: 51,735

[30] Foreign Application Priority Data Aug. 14, 1973 FOREIGN PATENTS OR APPLICATIONS 992,443 5/1965 Great Britain 102/30 1,078,272 8/1967 Great Britain 6,501,856

8/1965 Netherlands 102/30 Primary Examiner-Verlin R. Pendegrass Attomey-Gordon W. Hueschen and Talivaldis Cepuritis 57 7 7 ABSTRACT Finely-divided calcium chloride and/or magnesium chloride are employed to suppress and remove dust and noxious gases generated during blasting by sealing the blast-holes with these salts.

6 Claims, No Drawings METHOD FOR FIGHTING DUST AND NOXIOUS GASES AFTER BLASTS IN MINES BACKGROUND OF THE INVENTION The objective of the present invention is to fight effectively dust and harmful gases forming after blasts in mines, especially underground. Large quantities of dust and harmful gases originate, as is known, from blasting in coal, ore and mineral mines. Dust and noxious gases are a great nuisance and a health hazard to miners. Accordingly, blasts were often carried out when only a reduced number of men were at work or at the end of a shift. This, however, delayed the working of the mine.

Therefore, it is desirable to precipitate, as quickly as possible, the dust rising after blasts. The three principle methods are employed in the art for accomplishing this and are blasting behind a screen of fog, introducing cartridges filled with water, or introducing cartridges filled with cellulose-water-paste into the blast-holes. All three methods are equally effective, according to an essay by Landwehr and Bauer, published in Bergbau" No. 7, on pages 19] to 202.

Blasting behind a screen of fog is the most costly and difficult way. In the gallery, some yards behind the blast-hole, water and air are atomized, thus forming a zone of fog, behind which water only is atomized forming a precipitation zone. The nozzles required for this must be carefully serviced. Only then will this process be fully effective. However, the large quantities of water used increase the humidity of the air in the mine. Moreover, these large quantities of water will cause the floors of slaty mine galleries to swell. Because of the technical difiiculties and expenses involved, blasting behind a fog screen has been superseded by the use of cartridges filled with water or paste. These cartridges are polyethylene hoses, sealed at both ends. They are filled with water or a cellulose-water-paste and are introduced into the blast-holes behind the explosive charge. These cartridges are also useful to close up blast-holes. This process, as compared with the use of loam, allows to reduce by about 30 to 50 percent of the dust particles smaller than microns according to type of rock which reach the lungs and are therefore particularly harmful. Other possibilities to suppress dust rising after blasts have been examined too, as can be read in the publication cited, as well as in another one of Landwehr which appeared in Nobelhefte (May 196] pages 89 to I13. For example: Blowing in sand or introducing wetted limestone powder into the blast-holes. Both processes may be helpful in reducing the amount of dust, if circumstances are favorable. Their effect, however, is not satisfactory. The binding of dust by the limestone powder, for instance, is very much dependent upon the humidity content of the latter. For psychological reasons sand and limestone powder should not be'used in fighting dust as these materials are regarded as harmful, if used under different circumstances, and miners may loose confidence in the measures taken.

Furthermore, in his dissertationGrobdisperse Salzlosungs-Aerosole zur praktischen Feinstaubbekampfung im Steinkohlenbergbau (Clausthal, 1959), Mr. Leimroth quotes that the dust rising after blasts can be precipitated quickly by atomizing sodium chloride solutions containing 3% NaCl. This process, however, has the same disadvantages as the blasting behind'a screen of fog, even taking into consideration that only smaller quantities of water are required. This process has therefore not been adopted by mines. According to the Bergkademie (Freiberg) No. 16, (l964), pages 740 to 745, cartridges have already been used to fight dust. These cartridges, filled with aqueous magnesium chloride solutions, solutions of wetting agents or with salt respectively, were introduced into the blast-holes. It was found that when magnesium chloride solutions or solutions of wetting agents were used as compared with cartridges filled with water only the dust precipitation obtained was only slightly higher. The precipitation of dust was substantially less with sodium chloride. These substances will therefore not be widely used.

The measures cited are only useful to fight dust rising after blasts. The gases appearing in addition to the dust, especially carbon oxide and nitric oxides, cannot be removed by aforementioned measures as can also be seen in Nobelhefte (July 1965 pages 154 to 159. Before work can be resumed, however, it is necessary to wait until clouds of dust and gases become rarefied by the air and are carried away by the air stream.

According to the essay of Bryljacow published in Gornyj-Zjumal," No. 12, pages to 58, trial blasts with small amounts of explosives (2 kg) were carried out to examine possibilities for fighting harmful gases. Vials, filled with powdery sodium carbonate, gelatinous silica, chloride of lime, slaked lime or pyrolusite, were introduced after the explosive cartridges, sealing off the blast-holes. The reduction of rioxious gases, carbon oxide and nitric oxides was measured and compared to values obtained when clay was used. The quantity of harmful gases was reduced by 17 percent to 37 percent when gelatinous silica was used and by 48 percent to 56 percent when pyrolusite was employed. Valves obtained with the other substances were found to be between these figures. Similar results were obtained when hydrogen peroxide in solution or chloride of lime in solution, contained in vials were used, or when water was I introduced by means of pressure to seal off blastholes.

It was also attempted to introduce oxidizing agents such as potassium permanganate, manganese dioxide directly into the explosion cartridges. A reduction of the quantity of poisonous gases could thereby be observed. Trial blasts showed that the reduction of harmfulgases by the use of said substances are not satisfactory since, compared to water, the improvements were negligible. In spite of the water and the paste used both of equal value symptoms of poisoning as a result of blasts lately have been observed in miners.

To eliminate these adverse effects on miners and to make it possible that work can be resumed soon after the blasts are carried out, possibilities were searched for which would allow to fight more effectively dust and harmful gases rising after blasts.

SUMMARY OF THE INVENTION The method of this invention removes dust and harmful gases rising afier the blasting in mines. This method, based on the'use of salts, is distinguished from the prior art by the use of finely powdered calcium chloride and /or magnesium chloride to seal ofi blast-holes.

DESCRIPTION or THE PREFERRED EMBODIMENTS The fineness of the material used in accordance with the invention is preferably such that more than percent by weight are finer than l min and 60 percent by weight finer than 0.3mm. The water content of the calcium chloride or magnesium chloride respectively may be between 55 and percent by weight, i.e., hexa-, tetra-, di-, mono-hydrates and practically anhydrous substances can be employed.

To render the chlorides of the calcium or magnesium more effective, wetting agents, in particular non-ionic wetting agents like alkyl-phenol-polyglycolether may be added. The addition of alkaline reacting substances such as calcium oxide, calcium hydroxide, calcium carbonate, dolomite, sodium hydroxide, sodium hydrogen carbonate, sodium carbonate, potassium hydroxide, potassium carbonate, potassium hydrogen carbonate, urea and similar substances also proved useful. Calcium chloride or magnesium chloride treated with ammonia, thus reacting alkaline, may also be used. The addition of oxidizing agents like manganese dioxide, potassium permanganate, has advantageous effects. Additionally, sodium chloride or another metal salt may be admixed with the materials introduced into the blast-holes.

The materials cited, to be used in accordance with the invention are preferably employed in cartridges measuring to 30 cm made of plastic materials, e.g., polyethylene. Their caliber will be adapted to the caliber of the blast-holes. Once filled, both ends of these plastic hoses or pipes are hot-sealed or closed with a clasp etc. Cartridges may be bent or straight. The bent shape facilitates sealing of the blast-hole. Every cartridge contains about 200 to 300 gms. of the material in accordance with the invention. The cartridges of the present invention have good storage and transportation properties. The use of these cartridges, as compared with processes known hitherto, does not necessitate additional efforts.

Applying the process of the invention, blasts are prepared in the usual way. Blasts may be carried out in rock, coal, ores or minerals. Explosive charges are introduced into the blast-holes, and afterwards the material in accordance with the invention. Materials not contained in cartridges are introduced into the blastholes by means of a pneumatic device. If the materials of this invention are used in cartridges, they may be introduced by hand into the blast-holes. The quantity of material used is nearly the same, whether filled into cartridges or not. To ensure perfect sealing of the blastholes the cartridges, in accordance with the invention, may have a bent shape. Their shape may also be straight if used with an appropriate lock. Another way would be to slit them open a little before introducing them into the blast-hole, so that part of the powder can leak out inside the blast'hole, thus sealing it off. Once the material is introduced into the blast-hole, the explosive charge may be ignited as usual.

The finely powdered calcium chloride or magnesium chloride apparently combine with the large amounts of water steam forming after the blast. In this way the steam is condensed much faster into water drops which contain liquid calcium chloride or magnesium chloride. This mixture is instrumental in quickly agglomerating the dust, thereby forming, particles too big to reach the lungs, also precipitating the dust where it rises. It was also found that nitrous gases dissolve much better in the forming solution than in water stream or small drops that consist of water only. To increase the solubility of nitrous gases in the forming solution, additional alkaline reacting substances may be introduced into the blast-holes in addition to calcium chloride or magnesium chloride. The quantities of alkaline substances may be varied for best absorption of nitrous gases. 2-10 percent of alkaline substances, contained in the material introduced into the blast-holes after the explosives, are generally sufficient to reduce, within a few minutes,'the concentration of nitrous gases, contained in the air after blasts, far below the harmful limit.

A further advantage, if the material is used in accordance with the invention, is the absorption of the precipitated dust which is retained, having been wetted by a solution of hygroscopic salts. On account of its content of hygroscopic salt the water in the precipitated layer remains bonded, preventing the dust from rising again after further blasts. This danger exists if the dust was precipitated by water only which would eventually evaporate. Moreover, humidity of air in mines will not increase if materials are used in accordance with the invention.

Increased humidity of air in mines will always be observed when water is applied in cartridges or is sprayed in the mine. However, such an increase of the relative humidity of the air leads to a higher moist temperature deteriorating thereby the quality of the air. This, of course, is not desired and especially not in warmer galleries situated at greater depth. lf materials, in accordance with the invention, are introduced into blastholes, the air in mines will practically not be altered.

EXAMPLE (COMPARATIVE) This example allows a comparison between the use of water on the one hand and the use of calcium chloride powder on the other.

in both cases the agent, i.e the water or the calcium chloride powder, was filled into cartridges consisting of polyethylene tubes. Both ends of these tubes were heatsealed. Each cartridge contained 250g. of water or calcium chloride powder, respectively.

In the end plane of a galley in a coal mine, 16 holes were drilled. These holes were filled with explosive in a quantity of 1.5 kg explosive per 1 m of coal. Each hole was closed with one of the before-mentioned cartridges, in the first case all filled with water and in the second case all filled with calcium chloride powders. The velocity of the air supply was 0.7 m/sec. or 170 m lmin. The concentrations of the nitrous gases, NO,, and of the dust was measured at a distance of m from the end plane of the gallery and in periods of 30 seconds beginning with the time of ignition. The concentrations of the nitrous gases and of NO, were measured by absorption tubes according to standard procedure (System Traeger) and the concentration of the dust was determined with a Tyndalloscope. The results of thetests with the Tyndalloscope correspond approximately to the dimension of mg/m (dust/air).

The improvements effected according to the method of the invention are obvious from a comparison of the figures collected in parts I and 2 of Table l. Figures substantially the same as those in part 2 are obtained when employing magnesium chloride powder instead of calcium chloride powder.

it is to be understood that the invention is not to be restricted to the exact materials and procedures shown and described as the substitution of various equivalents will be apparent to one skilled in the art, wherefore the invention is to be limited only by the scope of the appended claims.

TABLE I COMPARATIVE l. Cartridges filled with water (prior art procedure) Period of time past Concentrations Concentrations the ignition, min. of nitrous gases of NO Dust m m s 0.5 0 20 L0 0 0 20 L 0 0 80 2.0 80 3 150 2.5 430 35 I70 3.0 600 50 l90 3.5 520 60 I90 4.0 300 20 180 4.5 200 5 I30 5.0 U5 2 85 5.5 30 0 75 6.0 20 0 70 6.5 l0 0 60 7.0 8 0 55 7.5 3 0 40 8.0 l 0 40 2. Cartridges filled with calcium chloride powder Period of time past Concentrations Concentrations the ignition, min. of nitrous gases of NO, ust p p g/m) 0.5 0 20 L0 0 0 20 1.5 0 0 50 2.0 50 2 I10 25 I50 5 l 10 3.0 225 10 l l5 I claim:

1. A cartridge adapted to seal off a blast hole and to suppress dust and harmful gases generating during blasting which consists essentially of an elongated plastic tube containing finely-divided solid particles of an alkaline earth metal salt selected from the group consisting of calcium chloride and magnesium chloride, said tube being closed at both ends.

2. The cartridge of claim 1 additionally containing an alkaline reacting compound.

3. The cartridge of claim 1 additionally containing an oxidizing agent.

4. The cartridge of claim 1 additionally containing sodium chloride.

5. The cartridge of claim 1 additionally containing a wetting agent.

6. The cartridge of claim 10 having a bent shape. 

2. The cartridge of claim 1 additionally containing an alkaline reacting compound.
 3. The cartridge of claim 1 additionally containing an oxidizing agent.
 4. The cartridge of claim 1 additionally containing sodium chloride.
 5. The cartridge of claim 1 additionally containing a wetting agent.
 6. The cartridge of claim 10 having a bent shape. 